Materials that have low gas permeability coupled with high flexibility have numerous uses in industry. Automotive rubbers such as tires and hoses benefit from such materials because they decrease weight, while many non-automotive uses benefit from low gas permeability irrespective of weight improvement.
One of the main improvements sought by automobile companies is reduced fuel consumption. One way to accomplish this is to reduce vehicle weight, which translates into reducing the weight of vehicle components, i.e. using less material. For example, pneumatic tires contain an inner liner that seals air inside the tire. The inner liner is usually made out of butyl or halogenated butyl rubber. To use this material, the tire manufacturer must sandwich and additional rubber layer with low hysteresis loss between the inner liner and the tire itself. As a result using butyl rubber as an inner liner results in a weight penalty from the inner liner and from the additional layer. Therefore, an appropriate butyl rubber replacement for tire inner liners potentially provides a two-faceted weight improvement. First, the additional rubber layer may be dispensed with. Second, to the extent that the substitute inner liner weighs less than the butyl-based inner liner further weight reduction is achieved, as when the replacement liners have a gas permeability that is lower than butyl liners. Lower gas permeability allows similar gas containment while using a thinner liner thereby reducing weight. Similarly, lower permeability materials result in weight savings for hoses as well. Additionally, when more gas tight hoses are used on closed systems, both automotive and non-automotive, the systems require less maintenance. This is especially important for refrigeration systems, such as air conditioners, that contain ozone-layer-destroying gases. Material with low gas permeability benefits a variety of uses.
Usually, materials with lower gas permeability do not have sufficient flexibility to reliably adhere to tire carcasses or rubber hoses. Plastics usually have lower gas permeability than rubbers, but much less flexibility. This stiffness causes the plastic liner to be unable to track the underlying substrate's expansion and contraction due to temperature changes resulting in a failure of the substrate-liner bond or the liner itself. EP 0 857 761 A1 discusses a variety of attempts at using plastic-base materials as tire inner liners. U.S. Pat. No. 5,910,544 discusses the problem for rubber hoses, as well. The unifying factor in the prior art solutions is the use of a low-permeability resin or thermoplastic. For instance, instead of using a butyl liner for a tire, JP06040207 (filed Jul. 24, 1992) discloses a film comprising polyvinylidene chloride.
The disclosures in EP 0 857 761 A1 and U.S. Pat. No. 5,910,544 outline partial solutions to the problem. These disclosures teach a thermoplastic vulcanizate that satisfies low-permeability demands, by using traditional thermoplastics, and that satisfies durability-driven flexibility demands, by using entrained thermoset rubbers. But improvements in permeability/flexibility parameters have not been exhausted. Lower-permeability-higher-flexibility materials are still needed.